Appdenix A. Realy Contact Protection Circuits
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Appendix A. Realy Contact
Protection Circuits
The contacts are the most important elements of relay constructions,
Contact performance conspicuously influenced by contact material, and
voltage and current values applied to the contacts.
Another important issue is contact protection, a right contact protection
circuit can suppress the counter emf to a low level. However, note that
incorrect use will result in an adverse effect. Typical contact protection
circuits are given below :
1. RC Circuit
This circuit is suitable for DC application. If the load is a timer, leakage
current flows through the RC circuit causing faulting operation.
Contact
Inductive
Load
R C
The below circuit is suitable for both AC and DC applications. If the load
is a relay or solenoid, the release time lengthens. Effective when
connected to both contacts if the power supply voltage is 24V or 48V
and the voltage cross the load is 100 to 200V.
Contact
Inductive
Load
R
C
Device Selection:
As a guide in selecting R and C,
R: 0.5 to 1
Ω
per 1V contact voltage